This invention relates to the field of rotating electric machines in general and, in particular, to a process for manufacturing a rotating electric DC machine, as specified in the preamble to claim 1, which is attached.
Rotating electric DC machines with a rated output below ca. 350 kW are generally designed to be uncompensated. This means that the stator of the DC motor is provided only with main poles for magnetization and commutating poles. It is the task of the commutating poles to make sure commutation occurs without harmful sparking at the edges of the brushes, since harmful spark formation results in high maintenance requirements due to abnormal wear on the brushes and commutator.
In most cases, DC motors with a rated output above ca. 350 kW are designed with compensating windings. This means that, in addition to the previously mentioned windings, the motor""s stator is also provided with a compensating winding. The coils of the compensating winding are placed in winding slots in the main poles, so that each coil of the compensating winding fills the slots of two adjacent main pole halves.
The compensating winding greatly reduces the so-called armature reaction. Without the compensating winding, the armature reaction causes a distortion of the magnetic flux in the main pole that is dependent on the direction of rotation, causing a degradation in performance. The compensating winding provides numerous advantages over the uncompensated DC motor. Examples of this include the following: greater utilization, i.e. a higher torque for a given rotor diameter; higher overload capacity; lower moment of inertia with otherwise identical performance; higher armature voltage and, thus, higher output power can be achieved because a higher mean lamination voltage is permissible without the risk of commutator sparking; better linearity between armature current and torque, which improves the possibility of regulating the load and rotational speed of the DC motor. The latter can be utilized, for example, to increase the so-called field-weakening region of the DC motor, i.e. the rpm range that is achieved by regulating the field circuit.
At the same time, however, the compensating winding creates a number of disadvantages, in the form of a cost increase of ca. 15-20% for the DC motor and reduced inductance, which leads to higher current ripple. This creates a higher noise level and, in certain cases, a DC motor that is more sensitive because of disturbances in the commutation process.
Customers"" performance needs are such that a compensating winding provides the optimal solution:
in rare cases, at powers under 350 kW;
in ca. 30% of the DC motors in the power range of 350-500 kW;
in ca. 50% of the DC motors in the power range of 500-1,000 kW;
in ca. 70% of the DC motors in the power range of 1,000-1,500 kW;
in practically all DC motors in the power range above 1,500 kW.
Because of the higher cost of compensating windings and the fact that it is not actually needed in many applications, DC motor manufacturers prefer to make DC motors with a variable design: uncompensated or with a compensating winding, depending on customer needs. This has been unprofitable with the conventional technology available, however, since the two design principles require significantly different rotor diameters for a given stator size. The space required by the compensating winding limits the rotor diameter for a given stator size.
With the solutions available using conventional technology, the compensating winding design determines the rotor diameter, if the idea is for the basic design to make possible both alternativesxe2x80x94uncompensated and compensated windingxe2x80x94in a single motor size (with the same center height). As a result, the rotor diameter in the uncompensated alternative is smaller than it could be if the motor were designed exclusively as uncompensated. The reduction is such that in approximately half the cases the performance can be achieved with a motor size smaller than the motor in an exclusively uncompensated design, which results in a more cost-effective solution, i.e. lower price/performance. For economic reasons, the limitations of conventional technology make it impossible to produce DC motors of the same motor size using alternative solutions: uncompensated and with compensating winding, respectively. In principle, this means that two totally different motors must be constructed for the two designs, with the accompanying tool costs and an increased number of versions to administer and to stock parts for. Thus, in practice, most DC motor manufacturers choose to make their motors exclusively uncompensated or compensated for a certain motor size.
The technical limitations of conventional technology result in costly compromises, both for motor manufacturers and for customers. The motors may be uncompensated, which results in unnecessarily large and expensive motors for handling high overloads, for example.
Uncompensated DC motors also have an unfavorable relationship between moment of inertia and performance, which means the motor must be overdimensioned for some applications. The alternative with compensating winding means that unnecessarily expensive motors are used in a large number of applications in which the performance requirements are modest. Due to the limitation of conventional technology described above, most DC motors over ca. 350 kW, regardless of the manufacturer, are made with compensating winding.
Considering the statements above, it is clear that no economically feasible solutions are available for creating the basic design of DC machines in such a way that, depending on the customer""s needs, the same machine size can be made either as uncompensated or compensated. Consequently, there is a great need to find an economically favorable solution that would make it possible, as needed, for machines of a certain size to be made as uncompensated or compensated, with no significant limitation on the rotor diameter and, thus, on the performance of either type of machine.
The invention eliminates the problems indicated above in an effective and suitable manner.
One general object of the invention is to bring about a solution to the problem of creating a rotating electric DC machine of a certain size, so that it can be produced at a reasonable cost for both an uncompensated design and with compensating winding.
Based on the considerations above, it is a basic object of the invention to find a simple means of additionally improving the power output of a compensated rotating electric DC motor of a certain size, i.e. with a certain center height, and, more specifically, to accomplish this using a method that, at an acceptable cost, will make it possible for a machine of the specified size to be made with an uncompensated design, with a rotor diameter that is maximal from the standpoint of its technical dimensioning, and with a compensated design, with just as large a rotor diameter as the uncompensated version.
In accordance with the invention, a process is made available for producing a rotating electric DC machine of the above-mentioned kind with which it will be practically possible to move the slots in the main pole of the machine for the compensating winding radially outward from the center of the stator to permit the optimal increase in rotor diameter. This is achieved by making the coil ends of the main coil taper radially outward. Thus, space is created in an advantageous manner for the compensating winding in the displaced slots, at the point where the compensating winding comes out of the winding slot. In another alternative or supplemental embodiment in accordance with this invention, additional space is made for the compensating winding where it comes out of the slots by angling the coil ends of the main coil radially outward.
In accordance with one embodiment of the invention, the outer turns in the coil ends are wound with a greater length than the inner turns in them. This produces the tapered shape in the coil ends in an advantageous manner.
In accordance with yet another embodiment of the invention, the coil ends of the compensating winding are angled radially outward outside the winding slots. In this way, it comes radially outside of the main coil, right at the outlet from the winding slots.
In accordance with another embodiment of the invention, the winding slots for the compensating winding in the main pole are shifted radially outward, so that they lie either mainly or completely radially outside those parts of the long sides of the main coil that are closest to the center of the stator.
In accordance with another embodiment of the invention, all the winding slots for the compensating winding are placed in the pole leg, namely such that all parts of the outer contour of the main pole""s pole leg lie outside a sector defined by the shaft center of the stator and the outer corners of the outermost winding slots in a main pole. In this way, the winding slots and the compensating windings placed in them place virtually no limits on the rotor diameter, neither by the direct risk of collision with the main coil nor by taking up room in the stator that is smaller in general due to a larger rotor.
By making the main poles in this way, it is possible in practice to eliminate the winding slots that are located closest to the main pole horns in a conventional stator. This reduces the degree of compensation, to be sure, but the reduced degree of compensation is offset more than sufficiently by the improved degree of utilization that is achieved by the increased rotor diameter provided by the present invention and by the noticeably reduced manufacturing cost of a compensated DC machine of a certain machine size. In this context, improved utilization generally means increased power output and torque relative to the machine size, i.e. the center height.
Another object of the invention is to provide a rotating electric DC machine with a compensating winding whose coils and the winding slots in them, with their compensating winding, are placed in accordance with the basic principles of the invention. Embodiments of this aspect of the invention are presented in the corresponding dependent claims.
An additional object is to provide a process for producing a stator for a DC machine in accordance with the basic principles of the invention. Embodiments of this aspect of the invention are presented in the corresponding dependent claims.
Another object of the invention is to provide a stator for a DC machine that is designed in accordance with the invention""s basic principles. Embodiments of this are presented in the corresponding dependent claims.
These and other objects of the invention are achieved by the invention as it is defined in the accompanying claims.
Another aspect of the invention relates to a use of a stator designed in accordance with the invention in an uncompensated DC machine. Such a use provides significant advantages, from the standpoint of standardization.
Additional aspects of the invention relate to a use of a stator designed in accordance with the invention in a motor or in a generator.
In summary, the present invention provides the following advantages over the conventional prior technology.
DC motors over ca. 350 kW, i.e. motors that with conventional design are normally compensated, can be make either uncompensated or compensated, with the same stator size.
In principle, the same stator laminations can be used to build stators in uncompensated and compensated machines of the same machine size which, in turn, allows
Savings in the manufacturing process which, in the power range of 350-1,000 kW, means cost savings of ca. 10% of the DC motor""s manufacturing costs, since the cheapest solution can be selected for each individual order, based on the customer""s requirements.
The payoff time is extremely short for the added investment costs needed to be able to make DC machines compensated or uncompensated, as the case requires. This means considerably greater future income and increased profit potential.
Increased rotor diameter and, thus, a significant increase in performance; the rated torque and rated power are increased by ca. 10% in compensated DC motors.
Other objects, specific features, and advantages of the invention are made clear by the dependent claims and by the description of the sample embodiments below.